Japanese Laid-open Patent Publication No. 2008-113446 discloses maintenance of a gradation of a middle-tone area in an original image inputted from various image input apparatuses and also automatic adjustment of a contrast between a black character and a ground in an output image without a user performing an operation, such as setting a parameter.
Japanese Laid-open Patent Publication No. 2008-79258 discloses a sharp reproduction of characters on a whiteboard or blackboard where illumination is reflected. For this, a luminance distribution histogram of image data is created to specify a background portion and a reflection portion of a whiteboard. A portion without characters and a portion with characters are then specified only for the reflection portion and characters contained in the reflection portion are reproduced to be sharp. The characters are reproduced while specifying the reflection portion, so that even in a portion which is saturated and in which a color difference is hardly presented, in the reflection portion, the portion without characters and the portion with characters can be surely discriminated without being affected by colors in other image portions.